average_bb_size.p7

We now have a pretty fast implementation, probably about as fast as we can get on a single core machine. However, on multi-core systems the cache line locking for the atomic operations becomes a bottle neck. To get around that we can use thread-private counts and aggregate them. With thread-private counts no locked instructions are needed, however the extra indirection does has its own cost of extra added instructions to spill a register and get the tls pointer so on single core this will be slower.

#include "dr_api.h"
+ #include <stddef.h>

#ifdef WINDOWS
# define DISPLAY_STRING(msg) dr_messagebox(msg)
#else
# define DISPLAY_STRING(msg) dr_printf("%s\n", msg)
#endif

#define TESTALL(mask, var) (((mask) & (var)) == (mask))
#define TESTANY(mask, var) (((mask) & (var)) != 0)

typedef struct bb_counts {
   uint64 blocks;
   uint64 total_size;
} bb_counts;

static bb_counts counts_as_built;
void *as_built_lock;

static bb_counts counts_dynamic;
+ void *count_lock;

/* Protected by the as_built_lock */
static uint64 bbs_eflags_saved;


static void
event_exit(void);
static dr_emit_flags_t
event_basic_block(void *drcontext, void *tag, instrlist_t *bb,
                  bool for_trace, bool translating);
+ static void
+ event_thread_init(void *drcontext);
+ static void
+ event_thread_exit(void *drcontext);

DR_EXPORT void
dr_client_main(client_id_t id, int argc, const char *argv[])
{
    /* register events */
    dr_register_exit_event(event_exit);
    dr_register_bb_event(event_basic_block);
+     dr_register_thread_init_event(event_thread_init);
+     dr_register_thread_exit_event(event_thread_exit);

    /* initialize lock */
    as_built_lock = dr_mutex_create();
+     count_lock = dr_mutex_create();
}

static void
event_exit(void)
{
    /* Display results - we must first snpritnf the string as on windows
     * dr_printf(), dr_messagebox() and dr_fprintf() can't print floats. */
    char msg[512];
    int len;
    len = snprintf(msg, sizeof(msg)/sizeof(msg[0]),
                   "Number of blocks built  : %"UINT64_FORMAT_CODE"\n"
                   "     Average size       : %5.2lf instructions\n"
                   "     Num saved eflags : %"UINT64_FORMAT_CODE"\n"
                   "Number of blocks executed  : %"UINT64_FORMAT_CODE"\n"
                   "     Average weighted size : %5.2lf instructions\n",
                   counts_as_built.blocks,
                   counts_as_built.total_size / (double)counts_as_built.blocks,
                   bbs_eflags_saved,
                   counts_dynamic.blocks,
                   counts_dynamic.total_size / (double)counts_dynamic.blocks);
    DR_ASSERT(len > 0);
    msg[sizeof(msg)/sizeof(msg[0])-1] = '\0';
    DISPLAY_STRING(msg);

    /* free mutex */
    dr_mutex_destroy(as_built_lock);
+     dr_mutex_destroy(count_lock);
}

+ static void
+ event_thread_init(void *drcontext)
+ {
+     /* create an instance of our data structure for this thread */
+     bb_counts *counts = (bb_counts *)dr_thread_alloc(drcontext, sizeof(bb_counts));
+     /* store it in the slot provided in the drcontext */
+     dr_set_tls_field(drcontext, counts);
+     memset(counts, 0, sizeof(bb_counts));
+ }
+
+ static void
+ event_thread_exit(void *drcontext)
+ {
+     bb_counts *counts = (bb_counts *) dr_get_tls_field(drcontext);
+     /* NOTE - if we so choose we could report per-thread sizes here. */
+     dr_mutex_lock(count_lock);
+     counts_dynamic.blocks += counts->blocks;
+     counts_dynamic.total_size += counts->total_size;
+     dr_mutex_unlock(count_lock);
+     dr_thread_free(drcontext, counts, sizeof(bb_counts));
+ }

static dr_emit_flags_t
event_basic_block(void *drcontext, void *tag, instrlist_t *bb,
                  bool for_trace, bool translating)
{
    uint num_instructions = 0;
    instr_t *instr, *where = NULL;
    bool eflags_saved = true;
+     bb_counts *counts = (bb_counts *) dr_get_tls_field(drcontext);

    /* count the number of instructions in this block */
    for (instr = instrlist_first(bb); instr != NULL; instr = instr_get_next(instr)) {
        /* Since it doesn't matter where we insert, look for a place
         * where the eflags are dead. */
        uint flags = instr_get_arith_flags(instr, DR_QUERY_DEFAULT);
        if (TESTALL(EFLAGS_WRITE_6, flags) && !TESTANY(EFLAGS_READ_6, flags)) {
            where = instr;
            eflags_saved = false;
        }
        num_instructions++;
    }

    /* update the as-built counts */
    dr_mutex_lock(as_built_lock);
    counts_as_built.blocks++;
    counts_as_built.total_size += num_instructions;
    if (eflags_saved)
        bbs_eflags_saved++;
    dr_mutex_unlock(as_built_lock);

    /* increment counters */
    if (eflags_saved) {
        where = instrlist_first(bb);
        dr_save_arith_flags(drcontext, bb, where, SPILL_SLOT_1);
    }
+     /* Spill a register to get a pointer to our TLS structure. */
+     dr_save_reg(drcontext, bb, where, REG_XDI, SPILL_SLOT_2);
+     dr_insert_read_tls_field(drcontext, bb, where, REG_XDI);
#ifdef X86_32
    /* Since the counters are 64-bit we must use an add an addc to increment.
     * The operations is still effectively atomic since we're only increasing
     * the count. */
    instrlist_meta_preinsert(bb, where,
!         INSTR_CREATE_add(drcontext,
!                          OPND_CREATE_MEM32(REG_XDI, offsetof(bb_counts, blocks)),
                         OPND_CREATE_INT8(1)));
    instrlist_meta_preinsert(bb, where,
!         INSTR_CREATE_adc(drcontext,
!                          OPND_CREATE_MEM32(REG_XDI, offsetof(bb_counts, blocks)+4),
                         OPND_CREATE_INT8(0)));

    instrlist_meta_preinsert(bb, where,
!         INSTR_CREATE_add(drcontext,
!                          OPND_CREATE_MEM32(REG_XDI, offsetof(bb_counts, total_size)),
                         OPND_CREATE_INT_32OR8(num_instructions)));
    instrlist_meta_preinsert(bb, where,
!         INSTR_CREATE_adc(drcontext,
!                          OPND_CREATE_MEM32(REG_XDI, offsetof(bb_counts, total_size)+4),
                         OPND_CREATE_INT8(0)));
#else /* X86_64 */
    instrlist_meta_preinsert(bb, where,
!        INSTR_CREATE_inc(drcontext,
!                         OPND_CREATE_MEM64(REG_XDI, offsetof(bb_counts, blocks))));
    instrlist_meta_preinsert(bb, where,
!        INSTR_CREATE_add(drcontext,
!                         OPND_CREATE_MEM64(REG_XDI, offsetof(bb_counts, total_size)),
                        OPND_CREATE_INT_32OR8(num_instructions)));
#endif
+     /* Restore spilled register. */
+     dr_restore_reg(drcontext, bb, where, REG_XDI, SPILL_SLOT_2);
    if (eflags_saved) {
        dr_restore_arith_flags(drcontext, bb, where, SPILL_SLOT_1);
    }

    return DR_EMIT_DEFAULT;
}

[ prev | next ]